This invention relates to dental trays for the production of a dental working model used for the preparation of a dental prosthesis.
In connection with the production of tooth crowns, tooth bridges, and the like, it is general procedure to form a casting mold which is used as a model base in the formation of the dental prosthesis. Dental die trays are frequently utilized for this purpose. The tray includes a mold cavity for use in the preparation of the model. Typically, after an imprint has been produced by the dentist in which the prepared teeth as well as possibly the gum, mandible portions, palate, etc. are imprinted, the imprint which represents the negative is filled by a special plaster mass at the laboratory or at the dental practice. At the same time, the mold cavity is filled up to its edges, and the imprint is layed onto the filled cavity to form a complete model. After the hardening, the complete model is generally removed from the mold and can be cut into sections for producing a dental prosthesis or portions thereof.
One of the requirements for utilizing such dental die trays, is the ability to reposition the cut model sections back into the mold cavity. Because the model can be cut into numerous pieces, each having a unique orientation, it may be difficult to find the proper location in the mold cavity from where the particular model section was formed, which can cause a problem in producing the dental prosthesis.
Another problem with existing die trays, is that when packing the mold cavity, it is not known if the entire mold cavity has been suitably filled with plaster material. Spaces may occur in the cavity where improper filling has occurred, and these spaces may produce weakening and imperfections in the model.
One improved die tray is described in U.S. Pat. No. 4,283,173. In this patented tray, the mold cavity is formed as a hollow portion which extends entirely through the tray. The mold cavity is shaped wider at the top than at the bottom, and also includes inwardly directed ribs along the mold cavity wall. The ribs are ramp shaped inwardly sloping from the bottom of the rib to the top of the rib.
Although the use of a hollow open-ended mold cavity facilitates packing of plaster into the mold cavity, there can still be difficulty in filling the entire mold cavity adequately. Also, although the tapered shape of the mold itself as well as the sloping shape of the ribs assist in relocating the cut model sections back into the mold cavity, there still can exist some ambiguity in their proper relocation. Furthermore, because of its resilience upon the slope of the rib, the height of the tray and the mold cavity therein must be sufficient to permit the development of the rib slope and the widening of the mold cavity which results in a thick dental tray from top to bottom.
Accordingly, while the use of a die tray is extremely important in the formation of a dental prosthesis, improvements in such die trays are needed in order to facilitate the packing of the mold cavity and to improve the relocating of the cut model sections back into the mold cavity.